Biology Reference
In-Depth Information
BOX 10.1
EMERGENCE PATTERNS OF A FAST GROWING
MAMMAL (TREE SHREW) AND A SLOW GROWING
MAMMAL (HUMAN)
In both tree shrews and humans, the
deciduous teeth (iimm) emerge prior to the
permanent teeth (I1, I2, M1, M2, M3).
However, in the tree shrew all of the perma-
nent molars emerge before the permanent
incisors. In humans, the incisors emerge
much earlier in the overall sequence. After
Smith (1994)
.
Rapidly growing animal: Tree shrew
wave 1:
iimm
M1 M2 M3
wave 2:
I1 I2
Slowly growing animal: Human
wave 1:
iimm
M1 M2 M3
wave 2:
)
I1 I2
Sequence Polymorphisms
Given the general sequence of emergence of human teeth presented above, there are char-
acteristic differences in the emergence sequences between human populations, which were
described early on by
Schultz (1940)
and Garn and colleagues (
Garn et al., 1962; Garn and
Lewis, 1963
). The differences in emergence sequences are called sequence polymorphisms
and are typically recognized in the written sequence by brackets surrounding the teeth
that change order in
15% of individuals examined within a species. The modern human
sequence is best described as [M1 I1] I2 [P3 C P4 M2] M3, indicating the tendency for M1
and I1 to reverse their emergence sequence and for the canine to alter the posterior emer-
gence sequence (it may appear before P3 or after P4 and in extreme cases, after M2).
Smith and Garn (1987)
demonstrated that there are differences in specific sequence poly-
morphisms between modern human groups. Utilizing data obtained from the Ten-State
Nutrition Survey
4
they were able to discern significant differences between the emergence
sequence polymorphisms present in female and male, and Black andWhite North Americans
(as defined by the categories used in the study) (
Smith and Garn, 1987
). This sample repre-
sents one of the few large enough for the establishment of population standards of emergence
sequence polymorphisms, none of which has been studied in this manner. We do not know,
for example, what the common sequence polymorphisms are for the majority of human pop-
ulations. Just as having specific population standards is necessary for accurate analysis of
skeletal remains, the study of dental samples that include a large number of subadults
4
The Ten-State Nutrition Survey was a federally funded study in the United States conducted between 1968
and 1970. Researchers collected anthropometric and dental growth data as well as clinical and nutritional
status of low-income children in ten states from various regions of the United States. (Ten-State Nutrition
Survey 1968
e
1970, 1972).
